more matrices

DavidLeoni · Oct 12, 2018 · 8946414 · 8946414
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diff --git a/commandments.ipynb b/commandments.ipynb
@@ -149,10 +149,10 @@
     "\n",
     "<div class=\"alert alert-info\" >\n",
     "\n",
-    "**COMMANDMENT 6: You shall never ever assign values to method calls**\n",
+    "**COMMANDMENT 6: You shall never ever assign values to function nor method calls**\n",
     "</div>\n",
     "\n",
-    "_WRONG WRONG STUFF:_\n",
+    "_WRONG WRONG:_\n",
     "\n",
     "```python\n",
     "\n",
@@ -162,7 +162,7 @@
     "\n",
     "```\n",
     "\n",
-    "_CORRECT STUFF:_ \n",
+    "_CORRECT:_ \n",
     "\n",
     "With the assignment operator we want to store in the left side a value from the right side, so all of these are valid operations:\n",
     "\n",
@@ -171,7 +171,7 @@
     "y = my_fun()\n",
     "z = []\n",
     "z[0] = 7\n",
-    "d = {}\n",
+    "d = dict()\n",
     "d[\"a\"] = 6\n",
     "```\n",
     "\n",
@@ -189,6 +189,159 @@
     "\n",
     "If there is no `return` in function description, the function is intended to return `None`. In this case you don't even need to write `return None`, as Python will do it implicitly for you."
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<div class=\"alert alert-info\" >\n",
+    "\n",
+    "**COMMANDMENT 8: You shall never ever redefine system functions**\n",
+    "</div>\n",
+    "\n",
+    "Python has system defined function, for example `list` is a Python type. As such, you can use it for example as a function to convert some type to a list:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 12,
+   "metadata": {},
+   "outputs": [
+    {
+     "ename": "TypeError",
+     "evalue": "'list' object is not callable",
+     "output_type": "error",
+     "traceback": [
+      "\u001b[0;31m---------------------------------------------------------------------------\u001b[0m",
+      "\u001b[0;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
+      "\u001b[0;32m<ipython-input-12-c63add832213>\u001b[0m in \u001b[0;36m<module>\u001b[0;34m()\u001b[0m\n\u001b[0;32m----> 1\u001b[0;31m \u001b[0mlist\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"ciao\"\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m",
+      "\u001b[0;31mTypeError\u001b[0m: 'list' object is not callable"
+     ]
+    }
+   ],
+   "source": [
+    "list(\"ciao\")"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "when you allow the forces of evil to take the best of you, you might be tempted to use reserved words like `list` as a variable for you own miserable purposes: "
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 13,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "list = ['my', 'pitiful', 'list']"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Python allows you to do so, but we do **not**, for the consequences are disastrous.\n",
+    "\n",
+    "For example, if you now attempt to use `list` for its intended purpose like casting to list, it won't work anymore:"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "```python\n",
+    "list(\"ciao\")\n",
+    "```\n",
+    "```\n",
+    "---------------------------------------------------------------------------\n",
+    "TypeError                                 Traceback (most recent call last)\n",
+    "<ipython-input-4-c63add832213> in <module>()\n",
+    "----> 1 list(\"ciao\")\n",
+    "\n",
+    "TypeError: 'list' object is not callable\n",
+    "\n",
+    "```"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<div class=\"alert alert-info\" >\n",
+    "\n",
+    "**COMMANDMENT 9: Whenever you introduce a variable with a for cycle, such variable must be new**\n",
+    "</div>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "If you read carefully Commandment 4 you should not need to be reminded of this Commandment, nevertheless it is always worth restating the Right Way.\n",
+    "\n",
+    "If you defined a variable before, you shall not reintroduce it in a `for`, since it is as confusing as reassigning function parameters.\n",
+    "\n",
+    "So avoid this sins:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 17,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "0\n",
+      "1\n",
+      "2\n"
+     ]
+    }
+   ],
+   "source": [
+    "i = 7\n",
+    "for i in range(3):  # sin, you lose i variable\n",
+    "    print(i)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 20,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def f(i):\n",
+    "    for i in range(3): # sin again, you lose i parameter\n",
+    "        print(i)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 21,
+   "metadata": {},
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "0\n",
+      "1\n",
+      "2\n",
+      "0\n",
+      "1\n",
+      "2\n"
+     ]
+    }
+   ],
+   "source": [
+    "for i in range(2):      \n",
+    "    for i in  range(3):  # debugging hell, you lose i from outer for\n",
+    "        print(i)"
+   ]
   }
  ],
  "metadata": {

diff --git a/exercises/basic-data-structures/basic-data-structures-solution.ipynb b/exercises/basic-data-structures/basic-data-structures-solution.ipynb
@@ -281,13 +281,6 @@
     "    \"\"\" Return D\"\"\"\n",
     "    raise Exception(\"TODO IMPLEMENT ME !\")"
    ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": []
   }
  ],
  "metadata": {